Underwater storage tanks have been used since at least as early as the Second World War for storing petroleum products underwater. During the 1940's, the primary purpose of maintaining underwater storage facilities was military, that is, to reduce the likelihood of destruction of the facility in the event of an air attack and to provide boats and ships with offshore refueling facilities so that they would not be required to return to port in order to refuel.
Today, underwater storage facilities generally have an entirely different primary purpose. The continued growth of offshore drilling and exploration, coupled with the necessity of exploring further from shore, often demands the ability to store the petroleum crude or processed petroleum at the drilling site. This enables the producer to store his output until a tank or barge load is collected, rather than have to pump it directly into a barge or other seagoing storage vessel on a daily basis. The latter would unnecessarily detain the vessel because one day's production is generally less than a full load.
Typically, a storage facility, according to the invention, can be provided which will store several days production output of an offshore facility. A barge or other vessel can then stop at the facility once a week or so to receive the contents of storage tanks.
In addition to the usual manufacturing problems with which the oil producer is faced on land, environmental considerations are now of considerable importance in connection with offshore drilling. Consequently, it is a paramount concern that adequate safety precautions be taken to prevent any leakage or spillage of petroleum into the sea. As a result, production facilities located offshore are generally equipped with elaborate systems to ensure that any seawater which becomes mixed with petroleum crude is filtered and cleaned prior to being returned to the sea.
It is therefore a primary object of this invention to provide an underwater storage assembly which is environmentally safe, which is easy to operate, which requires only modest pumping requirements, and which is capable of storing several days output of an offshore production plant. Further objects include providing an underwater storage assembly which is relatively simple to install, and simple to disassemble and clean as necessary.